In the field of this disclosure, spectral color management systems have been proposed that include multi-spectral image capture devices and multi-ink printers. In such a spectral color management system, a scene is captured by an image capture device (e.g., a multi-spectral digital camera), and a multi-ink printer generates printed output having spectral reflectance properties that are a good match to the spectral reflectance properties of objects included in the captured scene. By matching the spectral reflectance properties of the printed output with the spectral reflectance properties of the captured scene, the spectral color management system can generate printed output whose colors match the colors of original objects in the captured scene under different lighting conditions.
FIG. 1 shows an example workflow of a spectral color management system. A multi-spectral source device (e.g., a multi-spectral digital camera) generates a multi-spectral digital image of a captured scene. The generated image is represented in a device color space specific to the multi-spectral source device (i.e., source device color space 1). A forward source device conversion module 10 for the multi-spectral source device then converts the generated image into a spectral reflectance space 2, by using forward source device model 14. The spectral reflectance representation of the image is generated such that it represents the spectral reflectance of objects in the captured scene.
In particular, the spectral reflectance space 2 is typically determined algorithmically based on measurements of spectral reflectance of stimuli in a reference target and the corresponding response from the multi-spectral source device. Such measurements record the fraction of light reflected at a wavelength in the visual wavelength range that runs approximately from 400 nm to 700 nm. If the measurements of spectral reflectance are taken at every 10 nm in the wavelength range that runs from 400 nm to 700 nm, the spectral reflectance space 2 has a dimension of 31.
The spectral reflectance representation of the generated image is then further converted into an Interim Connection Space (ICS) 3 by an ICS conversion unit 11. The dimension of the ICS is taken to be an integer that is small relative to the dimensionality of spectral space 2, typically from 5 to 8.
A gamut mapping module 12 performs gamut checking to determine whether a spectral ICS value of the generated image is reproducible on an intended destination device, such as, for example, a multi-ink printer. A determination that a spectral ICS value of the generated image is reproducible on the destination device corresponds to an indication that the spectral reflectance of the captured image is reproducible on the destination device. The set of spectra reproducible on the destination device is called the spectral gamut of the destination device, and the data structure used to describe the gamut boundary is called the spectral Gamut Boundary Descriptor (GBD). The GBD contains descriptors for the gamut boundary. The gamut boundary is typically represented by continuous geometric constructs. A popular GBD construct is the convex hull, which is the smallest convex set in the ICS containing a set of sample points that span a gamut.
If the ICS value can be reproduced on the destination device, then the ICS value is passed to an inverse destination device conversion module 13 that converts the ICS data into the device color space 6 specific to the destination device, by using an inverse destination device model 15. If the ICS value cannot be reproduced on the destination device, then gamut mapping is performed using a GBD 4 of the destination device. Gamut-mapped data in the ICS 5 is passed to the inverse destination device conversion module 13 that converts the ICS data into the device color space 6 specific to the destination device.
In a case where the destination device is a multi-ink printer, the destination device uses the color image data in the device color space 6 to generate printed output having the spectral reflectance properties of the captured scene, such that the colors of the printed output match the colors of original objects in the captured scene under different lighting conditions.